The present invention relates to a magnetic recording medium having two magnetic layers. More particularly, it relates to a magnetic recording medium having an upper magnetic layer of a higher coercive force and a lower magnetic layer of a lower coercive force, which has improved sensitivity and frequency characteristics across broad frequency bands with less noise.
It has been known that in a magnetic recording medium having two magnetic layers, the sensitivity and frequency characteristics at both low and high frequency bands can be improved by making the coercive force of the lower layer low and that of the upper layer high. Such a magnetic recording medium is usually produced by first applying a magnetic paint composition containing magnetic particles of a relatively low coercive force onto a base film, such as a polyester film and drying the composition to form the lower magnetic layer, and then applying a magnetic paint composition containing magnetic particles of a relatively higher coercive force onto the lower magnetic layer and then drying the latter composition to form the upper magnetic layer.
However, a conventional magnetic recording medium of this type is produced by using almost the same particle size of .gamma.-Fe.sub.2 O.sub.3 particles in both the upper and lower magnetic layers, and hence, such recording medium shows insufficient improvement in lowering of noise level. Further, although in such magnetic recording medium, sensitivity and frequency characteristics at both low and high frequency bands are improved by a lower layer of lower coercive force and an upper layer of higher coercive force, it has such a drawback that the curve of the frequency characteristics slacks at the medium band, i.e., the frequency characteristics at the medium band drops. Particularly, although a magnetic recording medium having a lower layer of .gamma.-Fe.sub.2 O.sub.3 particles and an upper layer of CrO.sub.2 particles shows good characteristics, it has such a drawback that frequency characteristics thereof at the medium band is remarkably decreased, i.e., the magnetic recording medium shows considerable slack of frequency characteristics curve.